Networks for the communication of data between a central facility and a plurality of remote terminal devices are well known and may take many forms. A common form of the communication network is the loop configuration. In a loop communications configuration the stations in the loop are connected serially such that messages from the central facility pass serially through each station. The messages are coded so that the station to which the message is directed will be able to recognize the message as belonging to it. Likewise only one message at a time arrives at the central processor so that CPU overruns are unlikely even at a high throughput level. Loops do however manifest certain technical drawbacks. One of the more notable of these is that of the portable terminal. Whenever a terminal is unplugged from the loop to be moved, an unsophisticated loop system simply stops working because the series connection of the loop elements is broken. Further, power supply failure at a terminal can cause the repeating function at that terminal to fail and can also bring down the entire network. A third problem is that inadvertent or deliberate damage to any link can disrupt the operation of the entire loop.
A second type of communication network is the star configuration. In a star configuration each of the remote terminals is connected directly to the central processor for input and output. The most significant difficulty with a star configuration is that if it is operated in an asynchronous response mode the short term burst traffic at the central processor can easily exceed ten times the mean traffic rate so that the central processor must be overdesigned. Conversely, if the star configuration is operated by polling, the performance drops dramatically. The central processor can spend many more cycles servicing polls than messages, so it must still be overdesigned. A multidrop arrangement is confronted with traffic management difficulties similar to those of a star.